The present invention relates to improvement of a nuclear magnetic resonance apparatus having a controllable detector.
Detection of a nuclear magnetic resonance apparatus (hereinafter, abbreviated to NMR) is an operation for fetching a necessary signal from a voltage signal V(t). The voltage signal V(t) is induced to a probe coil by a magnetization vector rotating in a sample. The aforementioned detection operation is performed using a reference wave different from the voltage signal V(t).
The quadrature detection widely used as a detection method duplicates the voltage signal V(t), and multiplies each of them by reference waves Vr(t)=cos (ωrt) and V′r(t)=sin (ωrt), then filters them, thereby obtains a required signal.
The quadrature detection, for example, is described in Journal of Magnetic Resonance 14, 160 to 169 (1974). The digital quadrature detection obtained by applying a digital art to the quadrature detection to improve the defects thereof, for example, is described in Review of Scientific Instruments 70, 1511 to 1513 (1999).
In a conventional NMR apparatus for realizing the quadrature detection, the frequency ωr of the reference waves, at least during the execution of the detection operation, must be controlled so as to be kept at a fixed value. On the other hand, in the digital quadrature detection, the time interval Δ which is the time interval between data points of digitized NMR signals and also the time interval between data points of the reference waves, at least during the execution of the detection operation, is controlled so as to be kept at a fixed value.
In the apparatus for controlling the reference waves so as to keep at the fixed value, to prevent the quality of spectrums which are results of NMR measurements from reduction, various measuring conditions adversely affecting the voltage signal V(t) are also controlled so as to keep at the fixed values. The measuring conditions are, for example, the temperature of samples, the rotational speed of samples, and the static magnetic field intensity (generally called Bo magnetic field) given to samples by a magnet.
These arts, for example, are described In U.S. Pat. No. 5,192,910, U.S. Pat. No. 5,754,048, U.S. Pat. No. 4806868, and European Patent No. 692721. U.S. Pat. No. 5,192,910 discloses controlling the temperature condition constant, U.S. Pat. No. 5,754,048and U.S. Pat. No. 4,806,868 controlling the rotational speed of samples constant, and European Patent No. 692721 controlling the Bo magnetic field constant.